In 1866, German engineer Ernst Werner von Siemens (1823 – 1883) patented a dynamo with self-excitation. It was the basis for the initial development of the electricity industry, since it enabled the conversion of mechanical or thermal energy to electrical energy in devices with relatively low power. Since the original use of electrical energy, there was a huge progress towards far distance energy transfer. French electrical engineer, Marcel Deprez (1843 - 1918), was one of the firsts, who implemented DC transmission over greater distance. In 1873, he showed transmission between an engine and a dynamo to a distance of 1km, using a telegraph line.
At the time, first DC (direct current) electricity networks were built. They were used to enable production of electricity far from the location, where it is consumed (rivers, coal reserves, etc.). From the beginning, it was considered how to use the constructed power lines for transmission of messages. First, there was requirement to make possible transmission of control and management messages referred to the energy transfer. The AC (alternating current) power component was to be attached to DC voltage, which allowed creating a simple signalling system. It also required solving the compatibility of low-voltage control part with a high-voltage DC network, including safety equipment and handling.
Transmission of information in an AC electricity network could then be locally deployed with the use of DC pulses. However, these applications require additional DC sources and were very problematic in terms of equipment interconnections and compatibility with the lines. For this reason, they were soon replaced by systems transmitting AC signals with frequencies higher than the nominal frequency. The goal was to propose a simple signalization to control operation of these networks. Later on, there were simple systems for remote control, e.g. the network sectional disconnectors. It was always referred either to addressing the remote signalling of particular objects or addressing a single object from a remote command point, or a bi-directional combination of these systems. For these purposes, low-voltage networks were mostly involved; high-voltage networks - exceptionally.
At the same time, however, since the 30s of the previous century, there were Mass Remote Control (MRC) systems, which used to send a signal from one central location to branching high-voltage network, in which the group of remote-controlled devices were responding be sending either a common signal or a switching function.
Construction of robust and mechanically demanding long-distance high-power lines and very high power lines attracted the idea to use it for transmission of telephony. The very first attempts started to employ this principle also in power lines in the form of so-called high-frequency power telephony. In the Czech Republic, manufacturing of these devices started even before the Second World War in the company “Telegrafia Prague” (the predecessor of Tesla Strašnice). After the war, production of these devices continued.
Currently, however, there is growth of free high-voltage three-phase lines, where a specialty optical cable is incorporated in a protective metallic rope, which enables transmission of relatively huge data flow, comparable with ones that are common in conventional telecommunication networks with fibre optic cables.
Further development of telecommunications technology then enabled applications using low-voltage distribution parts of energy networks to create narrow-band systems, which are used for local control, signalling and remote measurements (e.g. Remote power meters reading). Advanced transmission technology, developed especially for the transmission of telecommunication signals in radio environments with high levels of interference also enabled the implementation of broadband data systems with high data transfer rates in a relatively harsh electromagnetic environment of electricity distribution networks.